Surface-active agents of the sulfobetaines family are known to exhibit good complexing properties with respect to divalent ions and are hence of particular interest for hydrocarbons recovery by chemical techniques using micellar systems.
The object of enhanced oil recovery is to increase the oil recovery rate, on the one hand, by a more regular scavenging of the field and, on the other hand, by a sufficient reduction of the capillary forces, particularly by decreasing the interfacial tension between the oil and the injected fluid, thereby increasing the efficiency of the microscopic displacement.
The efficiency of scavenging by water injection is generally improved by reduction of the water mobility, achieved by adding hydrosoluble polymers thereto. Several processes have been proposed to increase the efficiency of the microscopic displacement of the injected fluid: injection of solvents (hydrocarbon gases, carbon dioxide, alcohols, liquefied petroleum gas, etc . . . ), injection of alkaline water and solutions of surfactants in various forms: aqueous solutions, microemulsions, etc . . . . When using surfactants, usually in combination with hydrosoluble polymers, to stabilize the displacement, it appears that the recovery rate may reach 50% of the initial oil volume, and even, in favorable conditions, 70%.
A technique, now conventional, for decreasing the interfacial tension between the oil of the field and the injected fluid, consists of injecting a solution of surfactant whose characteristics are selected in relation with the conditions imposed by the field, particularly the water salt content, the nature of the oil in place and of the rock and the temperature. Then the injection of a hydrosoluble polymer solution is performed, followed with a water injection.
The surface-active compound is generally used at a concentration higher than the critical micellar concentration. The injected micellar systems are either aqueous solutions containing variable amounts of surfactants and, optionally, other additives such as co-surfactants, co-solvents, electrolytes, etc, or mixtures, in variable proportions, of water, electrolytes, hydrocarbons and, optionally, co-surfactants and/or co-solvents. In the latter case, the presence of polarapolar molecules at sufficient concentration leads to the formation of transparent mixtures, generally called microemulsions.
Many surfactant types have been proposed in the prior art for enhanced oil recovery. The most currently used surfactants, for reasons of cost and availability, are of the sulfonate type, more precisely petroleum sulfonates, as alkali metals or ammonium salts. The use of these surfactants is satisfactory as long as the water salt content does not exceed about 30 g/l (of sodium chloride equivalent) this value being given as order of magnitude: in particular, the interfacial tensions between oil and sulfonates solutions, obtained by a judicious selection of the product characteristics, are very low, about 10.sup.-3 mN/m, or even less. But, when the salt content substantially exceeds the above-mentioned value, it has been ascertained that the interfacial properties of sulfonates quickly degrade and the more as the content of divalent cations, calcium and magnesium particularly, is higher. Moreover, the high sensitivity of sulfonates to divalent cations produces, during the progress of the surfactant solution in the reservoir, precipitation and/or surfactant transfer phenomena in a stationary phase, which phenomena, associated with the release of cations by the rock, tend to make the surfactant inoperative.
It has been proposed to replace petroleum sulfonates with other types of anionic surfactants: for example paraffin-sulfonates, olefin-sulfonates, alkylsulfates, alkylphosphates, alkanoates, N acyl .alpha.-aminoalkanoates, carboxylates, sulfates and sulfonates of ethoxylated fatty alcohols and alkylphenols, etc . . . as well as non-ionic surfactants: for example ethoxylated fatty alcohols, ethoxylated alkylphenols, etc . . . .
However, these surfactants, substitute of petroleum sulfonates, suffer from a high loss in their interfacial efficiency, when the salt content of the field water is high. Non-ionic surfactants are much less sensitive than anionic surfactants to the presence of divalent cations with respect to the risk of precipitation. On the contrary, their major defect results from the fact that their properties in solution (low interfacial tension in particular) are very sensitive to small temperature variations. Moreover, the distribution of this type of product (distribution in relation with the polydispersity) between the different liquid phases is such that it results in a decrease of its useful concentration in the solution. Finally, the cloud point appears at relatively low temperature.
The mixtures of anionic and non-ionic surfactants have been the object of many laboratory works and the results show that such mixtures exhibit interesting interfacial properties, even in the presence of divalent ions; however, when using them in porous medium, there is an obvious risk of selective physi- or chemisorption which would quickly change the composition of the mixture.
In view of the various disadvantages of the conventional surfactants, researches have been conducted on the use of other surface-active compounds and, more particularly, on compounds of the zwitterionic type, products whose surfactant properties are not affected, or only to a small extent, by the presence of polyvalent cations, and this within wide temperature and pH ranges.
The idea to fix on the same surfactant molecule two different hydrophilic parts has been developed in various laboratories working on the problems of enhanced recovery. For example, the behavior of oxyethylated alcohols, modified at the end of the hydrophilic chain by a sulfonic group introduced through various techniques, as well as products resulting from the modification of the oxyethylated alcohol with chloracetic acid, have been studied.
In the prior art, the sulfobetaine surfactants are obtained generally by condensation of a tertiary amine (one alkyl group of which contains from 10 to 25 carbon atoms) with a sultone, propane-sultone or butane-soltone, according to equation 1: ##STR2## with Z=(CH.sub.2).sub.n and n=0 or 1.
The operation may also be conducted as described by R. G. Bristline, W. R. Noble and W. M. Linfield in J. Amer. Oil Chem. S. 53, 64, 1976 by reacting the same tertiary amines with the condensation product of epichlorhydrine on sodium bisulfite, according to equation 2: ##STR3##
The resultant hydroxylated sulfobetaines have an improved solubility.
The same authors indicate that the quaternization of the tertiary amines by means of allyl chloride, followed with the addition of sodium sulfite, also leads to sulfobetaines according to equation 3: ##STR4##
The condensation of ethylene sulfonic acid esters on tertiary amines salts have been disclosed, in the French Pat. No. 2 270 241, for manufacturing sulfobetaines according to equation 4: ##STR5##
Moreover, it has been proposed to synthesize sulfobetaines of improved solubility by introducing hydrophilic groups such as amide groups. In this respect, U.S. Pat. No. 4,259,191 discloses products obtained by reacting propane-sultones with amides-amines derived from naphthenic acids, according to equation 5: ##STR6## wherein R is a naphthenic acid remainder.
On the other hand, the surfactant properties of sulfobetaines and their excellent properties in hard waters have been mentioned and made obvious in several papers, such for example as the article of W. R. Noble and W. R. Linfield, J.A.O.C. 57, 368, 1980 and that of G. W. Fernley, J.A.O.C. 55, 98, 1978.
Their use in saline fields, containing in particular divalent ions, has been previously described. U.S. Pat. No. 4,216,097 discloses the use of a product complying with the formula: ##STR7## wherein R.sub.4 contains from 1 to 6 carbon atoms and A.sup..crclbar. is COO.sup..crclbar. or SO.sub.3.sup..crclbar., R.sub.1 being the lipophilic chain, but the longest R.sub.4 chain in the mentioned compounds comprises a methylbutylene group. In this patent, interesting indications are given on the efficiency at low concentration of this type of products and on their low adsorption, and it is particularly mentioned that the use of the product C.sub.16 H.sub.33 N.sup..sym. (CH.sub.3).sub.2 --CH.sub.2 --CH.sub.2 --SO.sub.3.sup..crclbar. provides for an excellent recovery in a medium of high divalent ions concentration.
As a whole, in the sulfobetaines of the prior art, the distance between the two zwitterion poles is determined by the nature of the sulfonic reactant and this distance is generally limited to four carbon atoms in linear chain.